Electric immersion heater for high temperatures



July 18, 1933. K. BADER 1,918,314

ELECTRIC IMMERSION HEATER FOR HIGH TEMPERATURES Filed March 13, 1931 a Qua/\- Patented July 18, 1933 UNITED STATES PATENT OFFICE KASPAR BADER, OF BERLIN-GRUNEWALD, GERMANY ELECTRIC IMMERSION HEATER FOR HIGH TEMPERATURES Application filed March 13, 1931, Serial No. 522,441, and in Germany March 17, 1930.

. Electric heaters are already known whose winding supports are made from ceramic material by various methods.

In most of theknown methods of manufacture the resistance is surrounded by a pulverulent ceramic insulating material which by using high pressure or heating the resistance imbedded in the ceramic material by electric current is compressed till it becomes solid or is baked to ether.

Heaters produced according to this method all have the defect that the ceramic material produced by the described process does notpossess such good properties as a ceramic material produced in a special glow furnace. Of course, with heaters produced according to this method the resistance wire is completely surrounded by insulation and protected against short circuits, whilst this is not the case with electric heaters having ceramic winding supports consisting of a plurality of separate parts. Ceramic winding supports produced according to the 1 a known method cannot however be employed for high working temperatures for the following reasons.

The ceramic material otherwise generally used in the heating industry is burnt for a number of days in a glow furnace at temperatures of 1,8002,000F C., and only thereby does it acquire its known good electrical v and mechanical properties. In contrast with this, the ceramic winding supports produced according to the above mentioned method are incomplete, as they cannot be produced with the necessary high temperature, since the resistance material employed only sustains temperatures of 1,2001,400 C. at the most, whereas these temperatures are much too low for the correct concentration of the insulating material.

For this reason, according to the present invention, heaters which have to sustain higher temperatures are composed of a plurality of small cube-shaped ceramic winding supports which have already been prepared. Practice has shown that such. heaters are quite capable of sustaining continuous temperatures up to 900 C.

If the heaters are to be used as immersion heaters for heating liquids, metal baths and the like, the winding supports must be built into a tightly closing metal housing. If flexible sheeting is chosen for this purpose, the whole heater permits itself to be easily bent, because the small ceramic elements from which the winding supportis composed can yield.

As however most metals oxidize at 800- 900 0., it happens that much oxide (slag) breaks away from the walls of the envelope and falls in between the individual ceramic winding supports. Metal oxides are in themselves conductive of current, and as soon as this metal oxide sets up a bridge between resistance wire and housing, the result is a short circuit, i. e. destruction of the heater.

The subject of the present invention permits on the one hand the manufacture of closed heaters up to 900 C.., and on the other hand prevents oxide slag penetrating from the outer metal envelope. For this purpose the combined ceramic winding supports are surrounded with an extremely thin non-oxidizable covering of metal difiicult to fuse (chromium nickel, molybdenum, iridium sheeting). This sheeting has the same, or a higher, fusion temperature as the re sistance material, whilst the outer envelope may consist of a cheap iron or steel sheet ing. If the outer envelope were made of the same material as the thin covering, the latter would be unnecessary; but this ma terial is much too expensive and very diflicult to weld in stouter sheets. On the other hand the iron or steel sheeting used as the outer envelope is cheap and easy to work. Thus by the present invention the resistances and winding supports are protected from the oxide slag formed when the outer covering is welded together, and such heaters are capable of carrying the above mentioned temperatures without difiiculty.

An exemplary embodiment of the invention is illustrated in the accompanying drawing.

Figure 1 is a sectional view of an immersion heater with ceramic Winding support.

Figure 2 shows a ceramic heater with heating spirals drawn in.

The metal housing 1 is provided with a ceramic heating element 5 consisting of a plurality of small, sa cube-shaped bodies, the ceramic unit-s, which have a bore for receiving the heating spirals 7, being so arranged in series that their bores form con tinuous channels in which the heating spirals 7 are disposed. In order that no metal oxide shall be able to penetrate between the small ceramic Winding supports 5 when the heater is hermetically sealed by welding shut, a paper-thin foil 4 of a material with a high point of fusion, such for instance as chromium nickel, molydenum, iridium or the like is wound round the wind ing supports 5, so as to protect the whole heater against penetration of the peeling off metal of the envelope 2.

Heaters constructed according to the invention, for instance, immersion boilers for melting metal baths, can sustain continuous temperatures of 800900 C., as an oxidation of the outer metal housing can have no influence on the heater itself nor, on its winding supports 5 and heating spirals 7( If the metal housing is made of flexible material the seried ceramic bodies permit a large degree of flexibility of the heater.

I claim.

1. Electric immersion heater capable of producing and sustaining temperatures of 800 C. in the material being heated, comprising a plurality of ready-burn ceramic elements having apertures and arranged in at least one row to form at least one continuous channel, a resistance winding in said channel, a thin heat-permeable diilicult-ly oxidizable metal jacket around said elements, and a sealed housing of cheap oxidizable metal surrounding said jacket, whereby said jacket protects said winding from detached fragments of said housing.

2. Flexible electric immersion heater capable of producing and sustaining tem ratures of 800 C. in the material being eated, comprising a plurality of ready-burnt ceramic elements having apertures therein, said elements being arranged in rows to provide continuous channels, an electric resist ance winding located in said channels, a jacket comprising a thin foil of diflicultlyoxidizable metal enclosing said elements, and a sealed flexible housing of cheap oxidizable metal surrounding said jacket, whereby said foil protects said winding from detached fragnmnts of said housing.

KASPAR BADER.

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